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Am. J. Pot Res (2008) 85:85-92DOT 10.1007/S1223000890066

Willamette: A Chipping Cultivar with High Yieldand Specific Gravity, Low Incidence of Hollow Heartand Brown Center, and Suitability for Fresh-Market UsageA. R. Mosley . S. Yilma D. C. Hane . S. R. James.K. A. Rykbost C. C. Shock. S. L. Love D. L. Corsini.J. J. Pavek R. E. Thornton . B. A. Charlton.E. P. Eldredge . R. G. Novy. M. J. Pavek.N. R. Knowles . J. L. Whitworth . C. R. Brown.J. C. Stark . M. 1. Vales

Published online: 4 March 2008Potato Association of America 2008

Abstract Willamette (A091812-1), a high-yielding, round,white-skinned variety with good chipping qualities, wasreleased in 2003 by the Oregon, Idaho and WashingtonAgricultural Experiment Stations and the US Department ofAgriculture-Agricultural Research Service. Willamette wasselected at Powell Butte, Oregon in 1993 from a crossbetween NDA203I-2 and A86463-3. Willamette vines arerelatively large, vigorous and medium-late in maturity. Yieldsof Willamette were higher than Atlantic across a number ofwestern states (total yield: Willamette 60.6 Mg haH, Atlantic50.8 Mg ha-1 ). Willamette exhibited fewer internal tuberdefects than Atlantic tubers (i.e. hollow heart and brown

A. R. Mosley S. Yilma M. T. Vales (i)Department of Crop and Soil Science, Oregon State University,Corvallis, OR 97331, USAe-mail: isabel.valesoregonstate.edu

D. C. HaneHermiston Agricultural Research and Extension Center,Oregon State University,Hermiston, OR 97838, USA

S. R. JamesCentral Oregon Agricultural Research Center,Oregon State University,Madras, OR 97741, USA

K. A. Rykbost• B. A. CharltonKlamath Basin Research and Extension Center,Oregon State University,Klamath Falls, OR 97603, USA

C. C. Shock E. P. EldredgeMalheur Experiment Station, Oregon State University,Ontario, OR 97914, USA

center: Willamette 2.0%, Atlantic 8.7%), but had similarlevels of external defects. Willamette chips well from 10°Cstorage (Willamette chip color 1.4, Atlantic 1.6) but not from4.4°C. Tuber specific gravity is comparable to that ofAtlantic (1.084). Willamette tubers contain slightly lowerlevels of total glycoalkaloids (Willamette 3.1 mg 100 g1,Atlantic 6.8 mg 100 g') and vitamin C (Willamette 16.4 mg100 g 1 , Atlantic 21.7 mg 100 g') than those of Atlantic,but has similar levels of dry matter, protein, dextrose andsucrose. Compared to Atlantic, Willamette shows greaterresistance to Verticillium wilt and potato leafroll virus,similar susceptibility to early blight, foliar late blight,

S. L. Love J. C. StarkUniversity of Idaho, Aberdeen Research and Extension Center,Aberdeen, ID 83210, USA

D. L. Corsini J. J. Pavek R. G. Novy J. L. WhitworthUSDA-ARS, Aberdeen Research and Extension Center,Aberdeen, ID 83210, USA

R. E. Thornton M. J. Pavek N. R. KnowlesWashington State University,Pullman, WA 99164, USA

C. R. BrownUSDA-ARS,Prosser, WA 99350, USA

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86 Am. J. Pot Res (2008) 85:85-92

Erwinia soft rot and potato virus Y, and greater susceptibilityto tuber late blight and common scab.

Resumen Willamette (A091812-1), una variedad de altorendimiento, redonda, de piel blanca, buenas cualidades parahojuelas, fue liberada en 2003, por las Estaciones Expen-mentales Agricolas de Oregon, Idaho y Washington y elServicio de Investigación Agricola del Departamento deAgricultura de los Estado Unidos. Willamette fue seleccio-nado en Powell Butte, Oregon en 1993 de un cruzamientoentre NDA203 1-2 y A86463-3. Las plantas de Willamette sonrelativamente grandes, vigorosas de madurez media—tardia.Los rendimientos de Willamette son mas altos que los de'Atlantic' en varios estados del oeste (rendimiento total:Willamette 60.6 Mg ha 1 , Atlantic 50.8 Mg ha). Willamettetuvo menos defectos internos del tubérculo que Atlantic (ie.Corazón vacio y oscurecimiento central: Willamette 2%,Atlantic 8.7%), pero tuvieron niveles sirnilares de defectosexternos. Willamette produce bieri hojuelas de papa proce-dentes de almacenamiento a 10°C (color de hojuelas deWillamette 1 .4, Atlantic 1 .6), pero no procedentes de 4.4°C.La gravedad especIfica del tubérculo es comparable a la deAtlantic (1.084). Los tubérculos de Willamette contienenligeramente menores niveles de glicoalcaloides (Willamette3.1 mg 100 g', Atlantic 6.8 mg 100 g) y vitamina C(Willamette 16.4 mg 100 g', Atlantic 21.7 mg 100 gpero tiene niveles similares de materia seca, proteina,dextrosa y sacarosa. Comparados con Atlantic, Willamettemuestra mayor resistencia a marchitez por Verticillium yPLRV, similar susceptibilidad al tizón temprano, tizón tardlofoliar, pudrición blanda causada por Erwinia y al PVY, ymayor susceptibilidad al tizón tardio al tubérculo y sarnacomün.

Keywords Solanum tuberosum . Variety . Chipping qualityBreeding

AbbreviationsRHSCC Royal Horticulture Society Color ChartPLRVPotato Leafroll VirusUSDAUnited States Department of AgricultureARSAgricultural Research Service

Introduction

Important traits associated with potato chip manufacturinginclude high tuber dry matter, low levels of reducingsugars, and freedom from internal and external tuberdefects (Dale and Mackay 1994). Round tubers with thinand smooth skin are preferred for chipping (Love et al.1998). Light chip color at harvest and after a period in

storage at temperatures approaching 10°C is preferred.Potato breeding efforts are increasingly focusing on thedevelopment of clones that produce light-colored chipsdirectly from cold (4-6°C) storage (Thill and Peloquin1995). In addition, genetic resistance to important pests anddiseases is highly desirable to minimize the costs associatedwith producing and managing the potato crop and to reducethe environmental impact of pesticides.

Willamette, tested as A091812-1, originated from ahybridization between NDA2031-2 (female) and A86463-3(male; Fig. 1) conducted by J.J. Pavek, US Department ofAgriculture—Agricultural Research Service (USDA-ARS),Aberdeen, ID, USA in 1991. NDA203I-2 produces light-colored chips directly from cold (4-6°C) storage (Love etal. 1998). Three of the grandparental lines are potatochipping varieties: Rosa (Plaisted et al. 1981), Kanona(Plaisted et al. 1989) and Norchip (Johansen et al. 1969).Rosa and Kanona have Solanuni tuberosun spp. andigenaclones in their backgrounds and are resistant to the goldencyst nematode (Globodera rostochiensis (Wollenweber)).Rosa also has resistance to early blight and potato leaf rollvirus (PLRV) and is moderately resistant to late blight.

Willamette was selected in 1993 at Powell Butte, OR,USA from single-hill plots. Subsequent evaluations foryield, quality and disease resistance parameters wereperformed in irrigated trials conducted throughout Oregonand in Western Regional trials from 1996 through 2000.Willamette was released in 2003 after 3 years of additionalevaluations and seed increase. Willamette was releasedmainly because of its high yield, light chip color from 10°Cstorage, high specific gravity, attractive tuber appearance

Wauseon

Rosa

J171-8NDA2O3 1-2

AND 16-1

ND41 3-4

WiIIamet ND9750-4(A091812-1)

Peconic

Kanorta

Bulk C N

A86463-3

04 731-1

Norchip.

M5009-2Fig. I Pedigree of Willamette (A091812- 1). Willamette resulted fromthe hybridization between NDA203I-2 (female) and A86463-3 (male)

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Am. J. Pot Res (2008) 85:85-9287

and adequate storage dormancy. Willamette providesgrowers with a medium-late variety with good chippingpotential. The smooth, round, attractive tubers of Will-amette may be used for fresh market in some situations.The variety name connotes the Willamette River Valley ofwestern Oregon. An application for plant variety protectionwas filed for Willamette in 2006.

Description

Plants

Growth habit: Medium height, upright, large vines (Fig. 2a,Table 1). Vine maturity is medium-late, 120 days afterplanting (Tables I and 2). Stems: Green with weak wings.

Table I Morphological characteristics of Willamette and Atlantic inWestern Regional trials, 1998-2000

CultivarYearVine sizeVine mat. 5Tuber shapec

Willamette1998L ML1.71999L ML1.82000M ML1.6Avg.L ML1.7

Atlantic1998M M 1.3999M EM1.2

2000M EM1.4AlT.MEM1.3

44 Medium, L large, E early (100-110 DAP), M medium (111-120DAP). L late (121-130 DAP)Vine size estimates

' Vine maturity (days after planting, DAP)Tuber shape estimates range from I =round to 5=long

Fig. 2 Willamette canopy (a),leaf (b), inflorescence (c), tubers(d) and light sprout (e)

AOMPOW

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Am. J. Pot Res (2008) 85:85-92

Table 2 Morphological characteristics of Willamette and Atlantic in Oregon trials, 1997-2000

Tuber parameters

CultivarYearVine mat.Shape Russ.'Skin colorEye depth'Size unifl'Shape unif. 5L/W ratioh

Willamette19974.3 1.21.12.0 3.7 3.7

3.7

0.9719983.8 1.11.12.3 4.2 3.8

4.3

0.9619993.9 1.71.42.0 3.8 3.1

3.3

0.9620003.8 1.21.52.3 3.7 3.2

4.2

0.97Average4.01.31.32.23.93.53.9 0.97

Atlantic19972.6 1.11.72.3 3.7 3.3

3.6

1.0019982.6 1.42.32.7 4.0 3.0

3.8

1.0319993.0 1.22.02.4 4.1 3.3

3.5

1.0120002.51.22.32.6 3.8 2.9

4.0

1.02Average2.71.22.12.53.93.13.7 1.02

'Vine maturity visual ratings: l=early; 2=early-medium; 3=medium; 4=medium-late; 5=lateb Tuber shape: range from 1=round to 5=long, narrowC Tuber skin russeting: range from l=light to 5=heavydTuber skin color: 1=red; 2=white; 3=buff; 4-brown; 5-dark brown

Tuber eye depth: range from I =deep to 5=shallowTuber size uniformity estimates: 1 =poor; 3=fair; Sexcellent

5 Tuber shape uniformity: 1=poor; 3=fair; 5=excellentTuber length to width ratio: 1 - round; 2=long, narrow

/

Leaves: dark green (Royal Horticultural Society ColorChart (RHSCC), 146A; Fig. 2b) with sparse mediumpubescence, open silhouette, green petioles and smallstipules. Terminal leaflet: Medium ovate with acuminatetip, cordate base, and no margin waviness. Primary leaflets:Three to four pairs; medium ovate with acuminate tip.Secondary and tertiary leaflets: Two to four in number.

Flowers

Four to six inflorescences per plant (average 4.5). Eachinflorescence has three to nine florets (average eight).Corolla: Purple-violet on inner surface (RHSCC, 82D),semi-stellate shape (Fig. 2c). Calyx: Regular symmetry andno anthocyanin pigmentation. Anthers: Yellow-orange

Table 3 Yield, grade and specific gravity of Willamette and Atlantic in trials conducted at four locations in Oregon, 1996-2000

Tuber yield

US no. 1

No.ofTotal

CultivarLocationyears(Mg ha-1)

Willamette Hermiston591.7K. Falls559.8Ontario558.2P. Butte546.3Average-64.0

AtlanticHermiston 560.6K. Falls453.6Ontario544.7P. Butte535.1Average-48.5

114-340g >340g(Mg ha)(Mg ha)

55.722.741.711.138.17.123.910.039.912.733.913.431.413.730.91.219.37.228.98.9

Total<114g(Mg ha') (Mg ha)

78.49.052.85.345.26.733.97.252.67.147.38.745.15.332.15.326.56.437.86.4

No. 2'sUSand cullsno. 1(Mg ha) (%)

4.3851.7886.3785.2734.48]4.6783.2847.3722.2754.377

TuberSpecificweightgravitya

(g)(g cmi)

216.21.078-1.085-1.091183.41.082199.81.084208.31.081-1.09-1.09178.31.091193.31.088

a Specific gravity was determined using the weight-in-air, weight-in-water method.

Ti Springer

59.562.859.660.643.158.151.350.8

49.452.548.050.033.046.942.740.9

8384818277818380

175.5172.6206.6184.9150.0161.3172.6161.3

1.0831.0791.0891.0841.0831.0871.0831.084

Willamette

Atlantic

199819992000Average199819992000Average

Am. J. Pot Res (2008) 85:85-9289

Table 4 Average yield and specific gravity of Willamette and Atlantic in Western Regional trials, 1998-2000

Tuber yield

US TuberTotal US no. 1 no.1 weightCultivar Year (Mg ha') (Mg ha') (%)(g)

Specific gravity'(g cm')

Specific gravity was determined using the weight-in-air, weight-in-water method

(RHSCC, 21A), broad-coned with intermediate pollenproduction. Stigma: Capitate, medium green (RHSCC,146A). Sty/ar length: Longer than anthers and straight.Low berry production.

Tubers

Round, intermediate in size (Tables I and 2), white(RHSCC, 158A) and smooth (Fig. 2d). The average tuberlength x width x thickness based on 20 randomly selectedUS No. I tubers at Corvallis, OR, USA was 78.3 mm(range from 60 to 90 mm, with 8.3 standard deviation)x78.5 mm (range from 60 to 85, with 5.9 standarddeviation)x71.4 mm (range 60 to 85, with 5.8 standarddeviation). The average weight per tuber was 199.8 g(Table 3). Eyes are shallow. The average number of eyesper tuber was 6.7 (range 5 to 8), and the eyes areconcentrated at the tuber apex. Eyebrows are slightly

Table 5 Average chip color and merit scores for Willamette andAtlantic in Western Regional trials, 1998-2000

Chip cobraChip color'CultivarYear(4.4°C)(10.0°C)Merit

Willamette19983.4 1.5 3.719994.2 1.5 3.820003.4 1.3 3.8Average3.7 1.4 3.8

Atlantic19983.1 2.0 2.819994.0 1.5 2.720003.7 1.4 2.5Average3.6 1.6 2.7

Color readings based on Snack Food Association chip colorstandards (I light and Sdark) following 3 months in storage at4.4°C and 10°C.b

Merit ratings based on estimates of overall cultivar performancerange from 1-worst to Sbest. (see: http://www.potatoes.wsu.edu!trials/documents/PotatoCultivarBook2 006 001 .pdf)

prominent. Tuber flesh is white (RHSCC, 158C). Tuberssometimes have folded bud ends (Fig. 2d).

Light Sprouts

Willamette light sprouts (Fig. 2e) are conical with weakpubescence and weak red-violet anthocyanin pigmentationat the tip of the base. The tip of the sprout is green, non-pubescent and has a closed habit. Some root initials arepresent at the base of the sprout.

Materials and Methods

Willamette was evaluated in irrigated trials throughoutOregon from 1996 through 2000. Trial sites includedHermiston, Powell Butte, Ontario, Klamath Falls andCorvallis. It was included in irrigated Western Regionaltrials from 1998 through 2000 at: Hermiston (early and lateharvests), Corvallis and Klamath Falls, Oregon; KernCounty, California; Aberdeen, Idaho; San Luis Valley,Colorado; Spring Lake Texas; and Othello, Washington.Trial and evaluation methods were similar but not identicalamong the many testing locations. Yield trials typicallyconsisted of four replicates of 25-ft single rows with 25 to33 seedpieces per plot arranged in a randomized completeblock design. Planting and harvest dates, fertility, irrigation,and pest management practices followed commercialrecommendations for the respective areas. Yield, grade,internal and external tuber defects, and quality evaluationswere performed using standard methods. Most cooperatorsmeasured tuber specific gravity by the weight-in-air/weight-in water-method. Storage temperatures varied slightly with4.4 and 10.0°C being typical. Chipping of US No. 1 tuberstypically occurred after 1 or 2 months of storage. Noattempt was made to systematically control storage relativehumidity. Reflectance readings for chip color were con-

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90

Table 6 Physiological defects of Willamette and Atlantic in Oregon trials, 1996-2000

Internal tuber defects

HH and BCIBSBSVD

CultivarLocationNo. of years % of tubers

WillametteHermistonKlamath FallsOntarioPowell ButteAverage

AtlanticHermistonKlamath FallsOntarioPowell ButteAverage

Am. J. Pot Res (2008) 85:85-92

External tuber defects

GCSB

Scale'

4.95.03.94.54.63.74.83.54.04.0

5 0.0

1.0

4.4

3.64.5

5 5.3

0.05.00.0

4.6

5 0.0

0.0

4.8

0.85.0

5 2.5 0.0

4.7

10.2

3.92.0 0.34.7

3.74.55 8.0

6.0

3.6

10.34.7

4 8.2

1.05.013.0

4.45 0.3

0.05.02.1

4.9

5 18.2

1.3

4.6

12.85.0

8.7 2.14.69.64.8

HH Hollow heart, BC brown center, BS blackspot bruise, VD vascular discoloration, lBS internal brown spot, CC growth cracks, SB shatter bruiseGrowth crack and shatter bruise estimates range from Isevere to 5-none

verted to Snack Food Association chip color scores. Meritscores were used to rate the overall performance in terms ofyield, quality, chipping potential, appearance and relatedfactors (See: http://www.potatoes.wsu.edu/trials/documents/PotatoCultivarBook2006 001 .pdf). Tuber dormancy wasevaluated in Corvallis, OR, USA after 2 months of storageat 10°C by calculating the percentage of sprouted tubersfrom a sample of 20 randomly selected US No. 1 tubers perreplication (four replicates). For all traits, Willametteperformance was compared to Atlantic (Webb et al. 1978).

Late blight (Phytophthora inJèstans) evaluations wereperformed under field conditions at Corvallis, OR, USA.Trials arranged in a randomized complete block design withfour replications were planted by the middle of June in 1999and 2000. Artificial inoculation of the plots with the US-8 lateblight strain was done in late August and early September and

Table 7 Physiological defects of Willamette and Atlantic in WesternRegional trials, 1998-2000

Internal defectsExternal defects

HH&BC IBS BS GCSB

CultivarYear% of tubers Scalea

Willamette19983.01.04.34.84.519990.60.03.64.94.020001.60.03.14.63.6Average1.70.33.7 4.84.0

Atlantic199816.35.04.04.33.9199914.41.93.94.83.2200015.02.33.74.93.3Average15.23.13.94.73.5

HH Hollow heart, BC brown center, IBS internal brown spot, BSblackspot bruise, GC growth cracks, SB shatter bruiseBlackspot bruise, growth crack and shatter bruise estimates range

from I = severe to 5-none

the trials were irrigated to encourage disease development.Under these conditions, most varieties were rated as extremelysusceptible to both foliar and tuber infection. Foliar infectionwas estimated by visually rating the percentage of foliageaffected using a 1 (no infection) to 9 (100% infection) scale.At harvest, ten tubers per plot were collected and stored forI month at room temperature in the dark to evaluate thepercentage of tubers visibly infected with late blight.

Verticillium wilt (early dying) and PLRV readings werebased on field plantings at Hermiston, Oregon, and Aberdeen,Idaho in 1999 and 2000. Potato virus Y (PVY) evaluationswere performed at Hermiston, Oregon, in 1999 under fieldconditions with high PVY disease pressure. Detection of PVYwas based on field symptoms as well as enzyme-linkedimmunosorbent assay (ELISA). Golden cyst nematode (G.rostochiensis) resistance bioassays were performed at Cor-nell University in Ithaca, NY USA by Dr. X. Wang using theRol pathotype. DNA-based evaluations using a markerlinked to the HI gene conferring resistance to the goldencyst nematode were conducted at Corvallis, OR, USA usingprotocols and primer sequences provided by Dr. W. DeJong.Other disease evaluations were conducted primarily byUSDA-ARS cooperators at Aberdeen, ID, USA.

Tuber composition evaluations from the Western Re-gional trials were performed at Aberdeen, ID, USA andincluded the following components: dry matter (solids,oven dry), protein, sugars (glucose and sucrose), ascorbicacid (vitamin C), and glycoalkaloids.

Agronomic and Quality Performance

In Oregon trials, Willamette averaged 64.0 Mg ha-1 totaland 52.6 Mg ha' US No. 1 (81% US No. 1) yieldscompared to 48.5 Mg ha-1 total and 37.8 Mg ha- ' US No. 1(77% US No. 1) yields for Atlantic (Table 3). In Western

IL Springer

Willamette

Atlantic

199819992000Avg.199819992000Avg.

22.624.824.223.922.725.623.724.0

6.65.45.45.86.75.65.96.1

0.030.020.010.020.040.020.010.02

0.190.230.220.210.150.210.160.17

15.218.715.416.419.323.722.221.7

5.12.22.03.17.76.26.56.8

Am. J. Pot Res (2008) 85:85-92

Vert. wilt ,Early blight

CultivarYear Scale

Willamette19992.4 6.720000.42.0Average1.44.4

Atlantic19993.76.720006.76.2Average5.26.5

Late blight

FoliarcTuber'Common scab"

2.510.02.09.038.034.05.824.018.06.50.04.09.03.09.07.81.56.5

91

Net necrosis'Erwjnja soft rotc

Scale

2.8 2.20.0 3.21.4 2.7

1.913.0 2.613.02.3

Table 8 Disease reactions for Willamette and Atlantic in Western Regional trials, 1998-2000

' Field readings at Hermiston, OR, USA and Aberdeen, ID, USAAberdeen, ID, USACorvallis, OR, USA

d Corvallis, OR, USA; percent of tubers visibly infected after 1 month of storageAberdeen ID, USA; percent with serious defects (more than 10% of tuber skin involved)Hermiston, OR. USA; percent of tubers with net necrosis from PLRVAberdeen, ID, USA

"Based on severity of foliar damage l=no symptoms; 21-5%; 35-10%; 4=10-20%; 5250%; 6=40-60%; 7=60_70%; 8 = 75-90%; 9=90-100% dead or dying with typical disease symptoms5 scale: 0-none; Imild symptoms not affecting grade; 2moderate symptoms with some culls due to disease; 3 = moderately severe symptoms,sample out of grade due to disease; 4=severe symptoms, sample out of grade: 5 = rnaximum severity, all tubers in sample show severe symptoms

Regional trials, a similar trend was observed (Table 4):Willamette produced 60.6 Mg ha-1 total and 50 Mg haUS No. I yields (82% US No. 1) versus 50.8 Mg ha' totaland 40.9 Mg ha-1 U.S. No. 1 (80%) yields for Atlantic.

Willamette tubers were larger (199.8 g) than Atlantictubers (193.3 g) in Oregon trials (Table 3) and also inWestern Regional trials (Willamette 184.9 g, Atlantic161.3 g; Table 4). The mean specific gravity for Willamette(1.084) was slightly lower than for Atlantic (1.088) inOregon Statewide trials (Table 3), but similar in WesternRegional trials (Table 4). Both Willamette and Atlanticproduced light chip color (1.4 and 1.6, respectively) after3 months of storage at 10°C (50°F), and both varietiesproduced unacceptably dark chips (3.7 and 3.6, respective-ly) when stored at 4.4°C (40°F; Table 5). Neither variety isconsidered to be a good 'cold chipper'. Willamette ranked

higher (3.8) than Atlantic (2.7) in subjective merit scores inall 3 years of Western Regional trials (Table 5), indicativeof its merit for fresh market as well.

Willamette tuber dormancy was greater than for Atlantic.After 2 months of storage at 10°C (50°F), Willametteshowed 76.3% sprouted tubers compared to 90% forAtlantic (significantly different at P<0.05). These resultswere based on one trial with four replications in Corvallis,OR, USA but are indicative of observed trends for alllocations.

Physiological Disorders and Resistance to Diseases

Willamette has typically shown a lower incidence ofinternal tuber defects, especially hollow heart and brown

Table 9 Relative tuber chemical composition of Willamette and Atlantic at Aberdeen, ID, USA 1998-2000

Dry matterProtein DWBDextrose FWBSucrose FWBVitamin C FWBTotal glycoalkaloids FWBCultivarYear

mg 100 g

Tubers grown at Aberdeen, ID, USA. Stored for approximately I month at 7.3-12.7 °C, cubed and freeze-dried prior to analysesDWB Dry weight basis. FWB fresh weight basis

IZ Springer

92

P.-

Am. J. Pot Res (2008) 85:85-92

Management

Management factors for Willamette have not been exten-sively studied. However, 3 years of evaluation at Aberdeen,ID, USA indicated moderate susceptibility to metribuzininjury. Post-emergence application(s) and high rates ofmetribuzin should be avoided with this variety.

Seed should be planted 15 cm deep and 24.1 to 30.5 cmapart within a row, with rows spaced 86.4 to 91.4 cm apart.Fertilization and irrigation practices should conform to thosefor a late maturing variety according to local practices. Foroptimum yield and quality, Willamette should be harvestedwhen mature, typically 10 days to 2 weeks later than Atlanticplanted at the same time. Mature tubers harvest will reducetuber skinning and the amount ofstolons clinging to the tubers.

Seed Availability

An application for plant variety protection is pending forWillamette. Enquire with local seed growers and the OregonFoundation Potato Sed Program for seed availability.

center (HH and BC) and internal brown spot, than Atlanticin Oregon and Western Regional trials and a similar level ofblackspot bruise (BS; Tables 6 and 7). Greatest differencesare evident for HH and BC: Willamette exhibited 2% and1.7% HH and BC in large-sized tubers in Oregon andWestern Regional trials, respectively, compared with 8.7%and 15.2% for Atlantic (Tables 6 and 7). In Oregon trials,Willamette also showed less vascular discoloration (3.7%)than Atlantic (9.6%). The two clones showed similar levelsof external defects, particularly growth cracks and shatterbruise, in both Oregon Statewide and Western Regionaltrials (Tables 6 and 7).

In 3 years of Western Regional trials Willamettedisplayed greater resistance to Verticilliuni wilt thanAtlantic (Willamette 1.4, Atlantic 5.2) and also greaterresistance to early blight (Willamette 4.4, Atlantic 6.5;Table 8), possibly because of its later maturity. Willamettewas also more resistant to tuber net necrosis caused byPLRV than Atlantic (Willamette 1.4%, Atlantic 13.0%).Willamette showed greater resistance than Atlantic to foliarlate blight in western Oregon in 1999 (2.5 versus 6.5), butthe cultivars were equally susceptible (9.0) in 2000.Willamette was more susceptible to late blight-inducedtuber decay than Atlantic (24% tuber damage in Willametteversus 1.5% Atlantic) and also more susceptible to commonscab (Willamette 18%, Atlantic 6.5%; Table 8). ELISAevaluations of grow-out plants at Hermiston, OR, USA in1999 (data not shown) indicated that both Willamette andAtlantic were susceptible to PVY. An allele associated withthe Hi golden cyst nematode resistance gene was present inWillamette (data not shown); however, bioassays performedby cooperators at Cornell University indicated that Will-amette is susceptible (11.8 cysts on average, range 6 to 15,standard deviation 4.4), indicating that there was recombi-nation between the molecular marker and the resistancegene or that the HI allele present in Willamette is noteffective against the golden cyst nematode pathotype Rolused in the bioassay.

Biochemical and Nutritional Characteristics

Willamette and Atlantic averaged the same percentage drymatter content (24%; Table 9). Willamette had lower levelsof tuber protein (5.8%), vitamin C (16.4 mg 100 g t ) andglycoalkaloicls (3.1 mg 100 g) than Atlantic (protein6.1%, vitamin C 21.7 mg 100 g and glycoalkaloids6.8 mg 100 g t ; Table 9). The percent of glucose wassimilar (0.02%) between the two varieties and the percentof sucrose was slightly higher in Willamette (0.21%) thanin Atlantic (0.17%; Table 9).

Acknowledgments We thank Dr. Xiaohong Wang and Dr. WalterDeJong for performing the golden cyst nematode bioassay and forproviding protocols to test for trait-marker association, respectively.Grateful recognition goes to the Foundation Potato Seed Program atOregon State University for producing tissue cultured plantlets andpre-nuclear seed stocks. The Oregon Agricultural Experiment Station,the Oregon Potato Commission, the USDA Cooperative StateResearch, Education, and Extension Service, and the USDA Agricul-tural Research Service provided financial support for this research.

References

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